{-# LANGUAGE CPP, BangPatterns #-}{-# OPTIONS_GHC -fno-warn-unused-imports #-}{- | Copyright : (c) 2010 Jasper Van der Jeugt
(c) 2010 - 2011 Simon Meier
License : BSD3-style (see LICENSE)
Maintainer : Simon Meier <iridcode@gmail.com>
Portability : GHC
'Builder's are used to efficiently construct sequences of bytes from
smaller parts.
Typically,
such a construction is part of the implementation of an /encoding/, i.e.,
a function for converting Haskell values to sequences of bytes.
Examples of encodings are the generation of the sequence of bytes
representing a HTML document to be sent in a HTTP response by a
web application or the serialization of a Haskell value using
a fixed binary format.
For an /efficient implementation of an encoding/,
it is important that (a) little time is spent on converting
the Haskell values to the resulting sequence of bytes /and/
(b) that the representation of the resulting sequence
is such that it can be consumed efficiently.
'Builder's support (a) by providing an /O(1)/ concatentation operation
and efficient implementations of basic encodings for 'Char's, 'Int's,
and other standard Haskell values.
They support (b) by providing their result as a lazy 'L.ByteString',
which is internally just a linked list of pointers to /chunks/
of consecutive raw memory.
Lazy 'L.ByteString's can be efficiently consumed by functions that
write them to a file or send them over a network socket.
Note that each chunk boundary incurs expensive extra work (e.g., a system call)
that must be amortized over the work spent on consuming the chunk body.
'Builder's therefore take special care to ensure that the
average chunk size is large enough.
The precise meaning of large enough is application dependent.
The current implementation is tuned
for an average chunk size between 4kb and 32kb,
which should suit most applications.
As a simple example of an encoding implementation,
we show how to efficiently convert the following representation of mixed-data
tables to an UTF-8 encoded Comma-Separated-Values (CSV) table.
>data Cell = StringC String
> | IntC Int
> deriving( Eq, Ord, Show )
>
>type Row = [Cell]
>type Table = [Row]
We use the following imports and abbreviate 'mappend' to simplify reading.
@
import qualified "Data.ByteString.Lazy" as L
import "Data.ByteString.Lazy.Builder"
import "Data.ByteString.Lazy.Builder.ASCII" ('intDec')
import Data.Monoid
import Data.Foldable ('foldMap')
import Data.List ('intersperse')
infixr 4 \<\>
(\<\>) :: 'Monoid' m => m -> m -> m
(\<\>) = 'mappend'
@
CSV is a character-based representation of tables. For maximal modularity,
we could first render 'Table's as 'String's and then encode this 'String'
using some Unicode character encoding. However, this sacrifices performance
due to the intermediate 'String' representation being built and thrown away
right afterwards. We get rid of this intermediate 'String' representation by
fixing the character encoding to UTF-8 and using 'Builder's to convert
'Table's directly to UTF-8 encoded CSV tables represented as lazy
'L.ByteString's.
@
encodeUtf8CSV :: Table -> L.ByteString
encodeUtf8CSV = 'toLazyByteString' . renderTable
renderTable :: Table -> Builder
renderTable rs = 'mconcat' [renderRow r \<\> 'charUtf8' \'\\n\' | r <- rs]
renderRow :: Row -> Builder
renderRow [] = 'mempty'
renderRow (c:cs) =
renderCell c \<\> mconcat [ charUtf8 \',\' \<\> renderCell c\' | c\' <- cs ]
renderCell :: Cell -> Builder
renderCell (StringC cs) = renderString cs
renderCell (IntC i) = 'intDec' i
renderString :: String -> Builder
renderString cs = charUtf8 \'\"\' \<\> foldMap escape cs \<\> charUtf8 \'\"\'
where
escape \'\\\\\' = charUtf8 \'\\\\\' \<\> charUtf8 \'\\\\\'
escape \'\\\"\' = charUtf8 \'\\\\\' \<\> charUtf8 \'\\\"\'
escape c = charUtf8 c
@
Note that the ASCII encoding is a subset of the UTF-8 encoding,
which is why we can use the optimized function 'intDec' to
encode an 'Int' as a decimal number with UTF-8 encoded digits.
Using 'intDec' is more efficient than @'stringUtf8' . 'show'@,
as it avoids constructing an intermediate 'String'.
Avoiding this intermediate data structure significantly improves
performance because encoding 'Cell's is the core operation
for rendering CSV-tables.
See "Data.ByteString.Lazy.Builder.BasicEncoding" for further
information on how to improve the performance of 'renderString'.
We demonstrate our UTF-8 CSV encoding function on the following table.
@
strings :: [String]
strings = [\"hello\", \"\\\"1\\\"\", \"&#955;-w&#246;rld\"]
table :: Table
table = [map StringC strings, map IntC [-3..3]]
@
The expression @encodeUtf8CSV table@ results in the following lazy
'L.ByteString'.
>Chunk "\"hello\",\"\\\"1\\\"\",\"\206\187-w\195\182rld\"\n-3,-2,-1,0,1,2,3\n" Empty
We can clearly see that we are converting to a /binary/ format. The \'&#955;\'
and \'&#246;\' characters, which have a Unicode codepoint above 127, are
expanded to their corresponding UTF-8 multi-byte representation.
We use the @criterion@ library (<http://hackage.haskell.org/package/criterion>)
to benchmark the efficiency of our encoding function on the following table.
>import Criterion.Main -- add this import to the ones above
>
>maxiTable :: Table
>maxiTable = take 1000 $ cycle table
>
>main :: IO ()
>main = defaultMain
> [ bench "encodeUtf8CSV maxiTable (original)" $
> whnf (L.length . encodeUtf8CSV) maxiTable
> ]
On a Core2 Duo 2.20GHz on a 32-bit Linux,
the above code takes 1ms to generate the 22'500 bytes long lazy 'L.ByteString'.
Looking again at the definitions above,
we see that we took care to avoid intermediate data structures,
as otherwise we would sacrifice performance.
For example,
the following (arguably simpler) definition of 'renderRow' is about 20% slower.
>renderRow :: Row -> Builder
>renderRow = mconcat . intersperse (charUtf8 ',') . map renderCell
Similarly, using /O(n)/ concatentations like '++' or the equivalent 'S.concat'
operations on strict and lazy 'L.ByteString's should be avoided.
The following definition of 'renderString' is also about 20% slower.
>renderString :: String -> Builder
>renderString cs = charUtf8 $ "\"" ++ concatMap escape cs ++ "\""
> where
> escape '\\' = "\\"
> escape '\"' = "\\\""
> escape c = return c
Apart from removing intermediate data-structures,
encodings can be optimized further by fine-tuning their execution
parameters using the functions in "Data.ByteString.Lazy.Builder.Extras" and
their \"inner loops\" using the functions in
"Data.ByteString.Lazy.Builder.BasicEncoding".
-}moduleData.ByteString.Lazy.Builder(-- * The Builder typeBuilder-- * Executing Builders-- | Internally, 'Builder's are buffer-filling functions. They are-- executed by a /driver/ that provides them with an actual buffer to-- fill. Once called with a buffer, a 'Builder' fills it and returns a-- signal to the driver telling it that it is either done, has filled the-- current buffer, or wants to directly insert a reference to a chunk of-- memory. In the last two cases, the 'Builder' also returns a-- continutation 'Builder' that the driver can call to fill the next-- buffer. Here, we provide the two drivers that satisfy almost all use-- cases. See "Data.ByteString.Lazy.Builder.Extras", for information-- about fine-tuning them.,toLazyByteString,hPutBuilder-- * Creating Builders-- ** Binary encodings,byteString,lazyByteString,int8,word8-- *** Big-endian,int16BE,int32BE,int64BE,word16BE,word32BE,word64BE,floatBE,doubleBE-- *** Little-endian,int16LE,int32LE,int64LE,word16LE,word32LE,word64LE,floatLE,doubleLE-- ** Character encodings-- *** ASCII (Char7)-- | The ASCII encoding is a 7-bit encoding. The /Char7/ encoding implemented here-- works by truncating the Unicode codepoint to 7-bits, prefixing it-- with a leading 0, and encoding the resulting 8-bits as a single byte.-- For the codepoints 0-127 this corresponds the ASCII encoding. In-- "Data.ByteString.Lazy.Builder.ASCII", we also provide efficient-- implementations of ASCII-based encodings of numbers (e.g., decimal and-- hexadecimal encodings).,char7,string7-- *** ISO/IEC 8859-1 (Char8)-- | The ISO/IEC 8859-1 encoding is an 8-bit encoding often known as Latin-1.-- The /Char8/ encoding implemented here works by truncating the Unicode codepoint-- to 8-bits and encoding them as a single byte. For the codepoints 0-255 this corresponds-- to the ISO/IEC 8859-1 encoding. Note that you can also use-- the functions from "Data.ByteString.Lazy.Builder.ASCII", as the ASCII encoding-- and ISO/IEC 8859-1 are equivalent on the codepoints 0-127.,char8,string8-- *** UTF-8-- | The UTF-8 encoding can encode /all/ Unicode codepoints. We recommend-- using it always for encoding 'Char's and 'String's unless an application-- really requires another encoding. Note that you can also use the-- functions from "Data.ByteString.Lazy.Builder.ASCII" for UTF-8 encoding,-- as the ASCII encoding is equivalent to the UTF-8 encoding on the Unicode-- codepoints 0-127.,charUtf8,stringUtf8)whereimportData.ByteString.Lazy.Builder.InternalimportqualifiedData.ByteString.Lazy.Builder.BasicEncodingasEimportqualifiedData.ByteString.Lazy.InternalasLimportSystem.IO(Handle)importForeign-- HADDOCK only importsimportData.ByteString.Lazy.Builder.ASCII(intDec)importqualifiedData.ByteStringasS(concat)importData.MonoidimportData.Foldable(foldMap)importData.List(intersperse)-- | Execute a 'Builder' and return the generated chunks as a lazy 'L.ByteString'.-- The work is performed lazy, i.e., only when a chunk of the lazy 'L.ByteString'-- is forced.{-# NOINLINE toLazyByteString #-}-- ensure code is sharedtoLazyByteString::Builder->L.ByteStringtoLazyByteString=toLazyByteStringWith(safeStrategyL.smallChunkSizeL.defaultChunkSize)L.Empty{- Not yet stable enough.
See note on 'hPut' in Data.ByteString.Lazy.Builder.Internal
-}-- | Output a 'Builder' to a 'Handle'.-- The 'Builder' is executed directly on the buffer of the 'Handle'. If the-- buffer is too small (or not present), then it is replaced with a large-- enough buffer.---- It is recommended that the 'Handle' is set to binary and-- 'BlockBuffering' mode. See 'hSetBinaryMode' and 'hSetBuffering'.---- This function is more efficient than @hPut . 'toLazyByteString'@ because in-- many cases no buffer allocation has to be done. Moreover, the results of-- several executions of short 'Builder's are concatenated in the 'Handle's-- buffer, therefore avoiding unnecessary buffer flushes.hPutBuilder::Handle->Builder->IO()hPutBuilderh=hPuth.putBuilder-------------------------------------------------------------------------------- Binary encodings-------------------------------------------------------------------------------- | Encode a single signed byte as-is.--{-# INLINE int8 #-}int8::Int8->Builderint8=E.encodeWithFE.int8-- | Encode a single unsigned byte as-is.--{-# INLINE word8 #-}word8::Word8->Builderword8=E.encodeWithFE.word8-------------------------------------------------------------------------------- Binary little-endian encodings-------------------------------------------------------------------------------- | Encode an 'Int16' in little endian format.{-# INLINE int16LE #-}int16LE::Int16->Builderint16LE=E.encodeWithFE.int16LE-- | Encode an 'Int32' in little endian format.{-# INLINE int32LE #-}int32LE::Int32->Builderint32LE=E.encodeWithFE.int32LE-- | Encode an 'Int64' in little endian format.{-# INLINE int64LE #-}int64LE::Int64->Builderint64LE=E.encodeWithFE.int64LE-- | Encode a 'Word16' in little endian format.{-# INLINE word16LE #-}word16LE::Word16->Builderword16LE=E.encodeWithFE.word16LE-- | Encode a 'Word32' in little endian format.{-# INLINE word32LE #-}word32LE::Word32->Builderword32LE=E.encodeWithFE.word32LE-- | Encode a 'Word64' in little endian format.{-# INLINE word64LE #-}word64LE::Word64->Builderword64LE=E.encodeWithFE.word64LE-- | Encode a 'Float' in little endian format.{-# INLINE floatLE #-}floatLE::Float->BuilderfloatLE=E.encodeWithFE.floatLE-- | Encode a 'Double' in little endian format.{-# INLINE doubleLE #-}doubleLE::Double->BuilderdoubleLE=E.encodeWithFE.doubleLE-------------------------------------------------------------------------------- Binary big-endian encodings-------------------------------------------------------------------------------- | Encode an 'Int16' in big endian format.{-# INLINE int16BE #-}int16BE::Int16->Builderint16BE=E.encodeWithFE.int16BE-- | Encode an 'Int32' in big endian format.{-# INLINE int32BE #-}int32BE::Int32->Builderint32BE=E.encodeWithFE.int32BE-- | Encode an 'Int64' in big endian format.{-# INLINE int64BE #-}int64BE::Int64->Builderint64BE=E.encodeWithFE.int64BE-- | Encode a 'Word16' in big endian format.{-# INLINE word16BE #-}word16BE::Word16->Builderword16BE=E.encodeWithFE.word16BE-- | Encode a 'Word32' in big endian format.{-# INLINE word32BE #-}word32BE::Word32->Builderword32BE=E.encodeWithFE.word32BE-- | Encode a 'Word64' in big endian format.{-# INLINE word64BE #-}word64BE::Word64->Builderword64BE=E.encodeWithFE.word64BE-- | Encode a 'Float' in big endian format.{-# INLINE floatBE #-}floatBE::Float->BuilderfloatBE=E.encodeWithFE.floatBE-- | Encode a 'Double' in big endian format.{-# INLINE doubleBE #-}doubleBE::Double->BuilderdoubleBE=E.encodeWithFE.doubleBE-------------------------------------------------------------------------------- ASCII encoding-------------------------------------------------------------------------------- | Char7 encode a 'Char'.{-# INLINE char7 #-}char7::Char->Builderchar7=E.encodeWithFE.char7-- | Char7 encode a 'String'.{-# INLINE string7 #-}string7::String->Builderstring7=E.encodeListWithFE.char7-------------------------------------------------------------------------------- ISO/IEC 8859-1 encoding-------------------------------------------------------------------------------- | Char8 encode a 'Char'.{-# INLINE char8 #-}char8::Char->Builderchar8=E.encodeWithFE.char8-- | Char8 encode a 'String'.{-# INLINE string8 #-}string8::String->Builderstring8=E.encodeListWithFE.char8-------------------------------------------------------------------------------- UTF-8 encoding-------------------------------------------------------------------------------- | UTF-8 encode a 'Char'.{-# INLINE charUtf8 #-}charUtf8::Char->BuildercharUtf8=E.encodeWithBE.charUtf8-- | UTF-8 encode a 'String'.{-# INLINE stringUtf8 #-}stringUtf8::String->BuilderstringUtf8=E.encodeListWithBE.charUtf8